The overall goal of this project is to determine the effect of dietary zinc deficiency on the immune response at different stages in development. The inbred A/J mouse will be used as a model for study. The results indicate that zinc deficiency causes rapid involution of the thymus in the young adult mouse. The antibody mediated response of the deficient animal was 1/5 to 1/10 that of mice fed zinc adequate diets. Examination of the functionality of T and B-cells indicated that T-cell helper function is severely impaired in the zinc deficient adult mouse while B-cell function remains intact for at least 4 weeks. Pair-fed studies indicated that zinc deficiency per se is responsible for thymic involution and impairment of T-cell helper function. However, if experimental feeding periods are prolonged such that there is a significant difference in body weight between the deficient and control mice, the reduced caloric intake will contribute significantly to the loss in immunity.